An ongoing integration of electrochemical impedance spectroscopy (EIS) into battery management systems shifts its use from lab efforts to real-world applications. To use the information from the EIS, mainly global model functions are defined to extract relevant parameters, requiring knowledge of cell behaviour and an overall spectrum to fit all necessary values.
This contribution focuses on the use of differential impedance analysis (DIA) as a tool for parameterising EIS to reduce computational effort. This principle is based on a local operator model (LOM), computed at each frequency measurement point in the spectrum and yielding the corresponding model parameters by deriving the values over the angular frequency. It consists of a serial resistance and an RC element to model the transient behaviour, which together form four individual parameters. The DIA further offers the advantage of combining cell-state-related parameter changes and model fitting while avoiding prior knowledge of the system’s general model behaviour.
Here, the DIA is used to represent the parameter behaviour of the LOM specifically and to map the system behaviour at different temperatures without making any significant physical statements.
It therefore shows a clear temperature dependence of the transient parameters. Additionally, it can help identify specific frequencies capable of detecting the cell’s temperature. The usability can be further enhanced by combining the DIA for multiple estimations. Here, the method could be integrated into SOH estimation and system modelling, as it avoids the need for a holistic model, which is particularly advantageous in cases of extreme SOC, where changes at the electrodes can significantly alter the impedance spectrum.